With such combine as above, grains obtained by threshing grain culms reaped by a reaping unit with a threshing unit are temporarily stored in a grain tank. When the grain tank becomes full, the grains will be discharged from the grain tank onto a truck, etc. A harvesting work on an entire agricultural field is carried out with repetition of storage to the grain tank and discharge from the grain tank described above. According to a combine disclosed in Japanese Unexamined Patent Application Publication Hei. No. 10-229740 (Patent Document 1), in response to an operation on a harvest weight (yield) switch, a weight obtained by subtracting a measured weight of empty grain tank from a measured weight of the grain tank storing grains is obtained as a grain weight (yield) inside the grain tank and displayed as such. With this combine, at the time of harvesting work traveling, a vehicle body horizontal control using a posture changing mechanism is executed, so that the vehicle body is maintained horizontal even on a sloped ground. For this reason, at the time of temporary vehicle stop for effecting a yield measurement, the traveling vehicle body and the grain tank are not necessarily under a parallel posture with each other. On the other hand, accurate weight measurement is not possible unless the traveling vehicle body and the grain tank are under a parallel posture. Thus, at the time of yield measurement, the vehicle body horizontal control will be deactivated and the relative posture between the traveling vehicle body and the grain tank will be shifted into the parallel posture by the posture changing mechanism. Incidentally, since the posture changing mechanism employs an actuator such as a hydraulic cylinder, when the posture changing mechanism is to be driven, it is necessary to raise the rotational speed of the engine sufficiently in advance acting as its power source.
Further, the combine is often equipped with an automatic reaping function configured to allow easy and high-accuracy harvesting operation by detecting unevenness in the field and automatically levelling the reaping height based on the detection and configured also to achieve energy saving by reducing the engine rotational speed to an idling rotational speed at the time of halt of the reaping operation. It is admitted that this automatic reaping function is convenient. However, if a yield measurement is to be effected during execution of the automatic reaping function, as the engine rotational speed is reduced in association with stopping of the vehicle body, an operation is needed for raising the engine rotational speed by deactivating the automatic reaping function, in order to allow the actuator of the posture changing mechanism to function fully.
A load cell used for detecting a weight of a grain tank is disposed generally between a lower portion of the grain tank and the vehicle body frame, as known from e.g. Japanese Unexamined Patent Application Publication No. 2013-118857 (see paragraph [0045], FIGS. 5 and 6) (Patent Document 2). In this way, if a weight detection is effected by the load cell between the portion affected by the weight of the grain tank and the vehicle body frame, the weight of grains inside the grain tank can be detected at any desired timing. Therefore, there is achieved an advantage of the ability to detect weight at any desired timing during a reaping operation, in comparison with an arrangement wherein an amount of grains inside a grain tank is detected by checking whether the grain amount has reached a predetermined level such as a full level or not, by means of an optical sensor a pressure-sensitive sensor disposed at an appropriate portion inside the grain tank. However, with the above-described arrangement of detecting the grain tank weight by a load cell, the grain tank weight detection is effected at a position laterally offset from the position where a bottom screw which is a massive and heavy constituent of the grain tank is present. Therefore, as the weight of the bottom screw per se is located at a position offset from the load cell, thus tending to apply a biased load to the load cell, accurate yield detection would be not possible in particular when the content amount of the grain tank is small, for instance.